With the increasing use of ceramic fiber insulation in order to conserve energy in electric furnaces, it has become apparent that there is a continuing need for reliable mounting systems for electric heating elements in furnaces insulated with ceramic fiber. There is a need for mounting systems which are suitable for use both with ceramic fiber modules and with ceramic fiber insulation in the form of blankets which are placed like wallpaper onto the furnace walls and held there with studs. There is a continuing problem with systems for holding electric hangers in furnaces insulated with ceramic fiber in that the hangers must possess strength to hold the electric heaters at high temperatures, but should not conduct significant heat to the shell of the furnace, should not distort the ceramic fibers or become dislodged during long-term use at high temperature and must not conduct electricity. The hangers further should be easily repairable. The problems with creation of reliable hangers for electrical elements are especially difficult at high temperatures such as above 1800.degree. F.
It has been proposed in U.S. Pat. No. 4,088,825 to Carr, that hangers for insulating members be held in place by anchors inserted between adjacent ceramic fiber bats and formed of electrically insulating material. A difficulty with this system is that it relies on the ceramic fibers to provide the strength. The hangers may distort the fibers, thereby opening up areas for heat to reach the shell and, further, it is not suitable for wallpaper type blanket insulation system. Further, the system requires large ceramic pieces which are expensive and provide weight which is likely to distort the fiber.
It has been suggested in U.S. Pat. No. 4,272,638 to Cimochowski, that electrical heaters be held by ceramic members which are placed against the furnace side of modules and held there by ceramic studs attached to the furnace housing. This system is very complicated and expensive. Further, it is generally not satisfactory for modules. Also, the system is difficult to install and is relatively heavy leading to possible distortion of the fibers.
U.S. Pat. No. 4,154,975 to Sauder discloses a system wherein electrical elements are supported by hooks attached to rods embedded in modules. This system also is expensive as the supporting elements must be preformed into modules in the desired locations. It further relies on the fibers themselves for structural strength which may cause difficulty at high temperatures. The system is difficult to install leading to high labor costs. It further relies on metal alloy hangers which may creep at high temperatures.
Another system has been proposed by Taki Industries Co., Ltd. of Japan which is a stud system utilizing insulating ceramic pieces to provide electrical insulation and utilizing direct welding of stud supports for alloy studs to the furnace wall. This also is a complicated system and under heavy weights has a bending effect on the alloy studs which may distort the fiber, especially at high temperatures.
Therefore, there remains a need for a simple, strong system of great mechanical integrity at high temperatures, particularly at temperatures above 1800.degree. F.